Being an American Express merchant for several of my business, I love accepting Amex, in fact, I'd rather have a customer use their Amex card than any other card, reasons are simple:
- Flat %, no "none qualified markups" live Visa & MC
- Amex card members just spend more, it's an indisputable fact
- Lower decline rate on service renewals
- No monthly fee to accept the card
- Very easy charge back resolution
- Excellent customer service
For these reasons alone, I'd prefer clients to use an Amex.